Diaper with Wet Diaper Monitoring Device

ABSTRACT

A diaper includes a diaper body and a wet diaper monitoring device, which includes a disposable pouch and a monitoring device. The monitoring device includes a monitoring casing, a first sensor electrode, a second sensor electrode, a sensing circuitry and an indicator. The first sensor electrode and the second sensor electrode are provided on an inner surface of and received in the monitoring casing, and form a single planar capacitor when the diaper body is dry. When the diaper body becomes wet, a capacitance between the first sensor electrode and the second sensor electrode increases substantially so as to transform the single planar capacitor of the first sensor electrode and the second sensor electrode into two much larger series connected capacitors.

BACKGROUND OF THE PRESENT INVENTION Field of Invention

The present invention relates to a diaper, and more particularly to adiaper comprising a wet diaper monitoring arrangement which is capableof detecting and alerting users when the diaper becomes wet.

Description of Related Arts

Two common wet diaper detection methods are used in prior arts. They areconductance sensor detection method and capacitance sensor detectionmethod. Conductance sensor detection method generally relies on thedetection of small amount of current flows across a sensing element whenwetness is detected. Typically, this type of sensing element consists oftwo parallel conductors or wires imbedded between an inside layer and anoutside layer of a diaper. Urine is a good conductive fluid. When thediaper is soiled, urine causes current to flow between the twoconductors or wires. Conductance sensor imbedded in the diaper layersrequires special manufacturing process that leads to high productioncost.

On the other hand, various capacitance sensor designs were discussed inprior arts. For example, the general capacitance sensor design principlewas described in U.S. Pat. No. 8,866,624 issued to Ales, III et al.,U.S. Pat. No. 5,903,222 issued to Kawarizadeh, and U.S. Pat. No.5,469,145 issued to Johnson. These referenced inventions used two ormore metallic electrodes etched on a standard or flexible printedcircuit board (PCB) forming a capacitor whose capacitance value dependson the dielectric constant (E) of the material between the twoelectrodes. The capacitance sensor is fastened on the outer surface of adiaper, so it could sense the change in dielectric constant of thediaper's inner layer when soiled. Dielectric constant of the diaper'sinner layer increases by a factor of 10 or more when soiled.

Four type of capacitor sensor detection methods are generally used inprior arts to detect capacitance change due to a wet diaper condition:

1. Detection of frequency shift in a LC resonant circuit or a RCoscillator circuit where sensor capacitance is part of the circuit;

2. Detection of impedance changes in a LC tank circuit where sensorcapacitance is part of the circuit;

3. Analog voltage amplitude detection of a sensor capacitance coupledsignal; and

4. Measure the rise time of the capacitance sensor using a precisioncurrent source.

The first three detection methods are inherently analog in nature andwhich are less precise and less repeatable than digital method.Furthermore, analog detection circuits are also need more power despitesome mitigating designs such as a low duty cycle detection method wherethe measurement circuit is only active for a very short period of time.Large power consumption is not desirable for a battery powered device.Rise time measurement method can either be analog or digital method. Aseparate analog to digital converter device is needed for digitalmeasurement method.

In prior arts, many monitoring device electronics and the sensingelement are two separate parts. They need to be linked together, bothmechanically and electrically, via simple mechanical connectors such asmetallic snap, clip or fastener. The monitoring device is typicallyclipped onto the diaper surface or the diaper edge. Therefore, theparent or caretaker must engage or disengage these mechanical connectorson every use. The process can be tedious, but it allows the monitoringdevice to be reused while discarding the disposable sensing element.

Due to the use of the snap and clip, most monitoring devices of thiskind are not protected against contamination by urine or feces in anaccidental spill. A thorough cleaning is required after such anincident—a process not very appealing to the parent or a care taker.

Other sensing elements proposed in prior arts include: chemical sensor,temperature sensor, optical sensor, etc. Most of these sensing elementsare not very popular primarily due to their high cost.

The following patents are pertaining to the present invention:

U.S. Pat. No. 5,469,145 to Johnson describes a wet diaper detector usingeither resistive sensor or capacitive sensor. When a capacitive sensoris used, the sensor couples a pulse signal to a voltage sensitivethreshold detection circuit. The coupled pulse signal is proportional tothe sensor capacitance. The threshold detection circuit consists of anop-amp and a voltage comparator. Op-amp amplifies the coupled pulses toa more suitable voltage level so it can be peak detected. The detectedpeak signal is fed to a voltage comparator for making voltage thresholddetection. This detection method is a pure analog in nature.

U.S. Pat. No. 5,903,222 to Kawarizadeh et al. describes an enclosed wetgarment detector using a capacitive sensor. This sensor and itsassociated electronics are placed inside a housing. However, it is notedthere is an air gap between the sensor electrodes the housing interiorsurface. Any such air gap would reduce sensor sensitivity as itsdielectric constant is very close to “1”.

It uses the same voltage threshold detection principle as the 145 patentwhere the coupled pulse signal by the sensor is amplified and peakdetected for voltage threshold detection. The circuit requires manualadjustments during production for proper circuit performance.

U.S. Pat. No. 8,866,624 to Ales, III et al. describes various open facesensor electrode designs and general methods to detect capacitancechange.

U.S. Pat. No. 9,241,839 to Abraham et al. describes a linear sensorarray to detect wetness level. Sensor array consists of severalidentical sensor electrodes arranged in a linear manner such thatdifferent part of a diaper can be monitored.

U.S. Patent application 2007/0024457 to Long et al. describes variousmechanical methods of removably affixing a device to the sensor element.

U.S. Pat. Nos. 8,416,088 and 8,111,165 to Ortega et al. describes apatient monitoring system for sensing pressure and wetness on a humanbody. It describes a device fabricated on a flexible circuit boardsubstrate, so the finished device can be adhered or placed on a humanbody. The device contains a signal processing circuit and a RFtransmitter circuit for sending a wireless signal to a remote receiver.A resistance sensor was described for urine detection.

U.S. Pat. No. 9,107,776 to Bergman et al. describes an elaborateincontinence management system and a custom designed diaper wherenumerous sensors were imbedded inside. The system provides a softwareestimate of a wetness event based on various sensor inputs. A resistancesensor was described, and it needs to encounter liquid such as urine tosense a wet condition.

U.S. Pat. No. 8,471,715 to Solazzo et al. describes a custom designeddisposable diaper with an imbedded resistance wire sensor and aremovable, reusable battery powered sensor-transmitter device. Thereusable sensor-transmitter portion must be manually connected to theimbedded resistance wire sensor after each diaper change.

U.S. Pat. No. 6,603,403 to Jeutter et al. describes a wetness monitoringmethod of an absorbent article consisting of an imbedded passivetransponder/sensor device which receives electrical energy from anexternal interrogator device. Both interrogator circuit andtransponder/sensor circuit must be near each other so that electricalenergy at a specific frequency can be transferred via an antennacoupling circuit within each device. This is essentially a RFID device(Radio Frequency Identification) with an external interrogationdetector.

U.S. Pat. No. 6,774,800 to Friedman et al. describes a patientincontinence monitoring apparatus using RFID tag technology where apassive RFID tag is placed on a disposable diaper. An externalinterrogation device is needed to provide an excitation signal to powerthe RFID tag. The same interrogation device must read and decode thereturn signal on the wetness condition of the diaper.

U.S. Pat. No. 8,314,284 to Novella describes a diaper change alertingdevice for a custom implemented disposable diaper with a built-in pouch.The pouch houses the electronic device and is made of liquid permeablematerial, so urine can enter. When urine permeates into the pouch, theelectronic device sensor detects a change in resistance or conductivityand acts accordingly to activate a built-in music speaker. Theelectronic sensor must be removed and cleaned before introduction into anew diaper.

U.S. Pat. No. 9,278,033 to Abraham et al. also describes an imbedded LCresonant circuit for RFID application. It requires an externalinterrogation device to detect the change in diaper wetness.

U.S. Pat. No. 7,145,053 to Emenike et al. describes diaper moistureindicator device with audible and display output. The invention isdesigned to clip onto a diaper outer surface. The invention relies onthe detection of resistance drop across two sensing terminals caused byurine intrusion into a measurement sensor gap. Both unit and its sensorneed to be cleaned after each use.

U.S. Pat. No. 6,870,479 to Gabriel describes a custom implementeddisposable diaper with built in wire mesh as a resistance sensor. A wetdiaper condition causes resistance to drop and a processor can detectsuch a change in resistance or conductivity.

U.S. Pat. No. 7,221,279 to Nielsen describes a monitoring systemconsisting of two portions: a disposable sensor unit and a reusablemonitor/indicator unit. Both units are electrical connected via aconnector. The sensor unit is essentially a resistance sensor placedinside a diaper, so it absorbs a small portion of any urine volume.

U.S. Patent application 2008/0278337 to Huang describes a urinedetection system utilizing two flexible printed circuit substrates withetched capacitance sensor electrodes. One circuit substrate is placedinside the diaper and the other is placed on the outside of the diaper,but the two substrates need to precisely align for maximum capacitanceeffect.

U.S. Patent application 2009/0124990 to Feldkamp et al. describes aninduction coil wetness sensor. The sensor consists of an LC resonanttank circuit. The tank circuit impedance changes as wetness levelincreases inside the diaper. The change is reflected on the DC outputlevel of a marginal oscillator circuit.

U.S. Pat. No. 9,820,891 to Eyall describes a capacitance and photodetector method to detect a soiled diaper condition.

Other reference patents which may be pertinent to the present invention:

U.S. Pat. No. 9,278,033 Abraham U.S. Pat. No. 9,241,839 Abraham U.S.Pat. No. 9,107,776 Bergman U.S. Pat. No. 8,866,624 Ales, III U.S. Pat.No. 8,111,165 Ortega U.S. Pat. No. 8,416,088 Ortega U.S. Pat. No.8,471,715 Solazzo U.S. Pat. No. 8,314,284 Novella U.S. Pat. No.7,221,279 Nielsen U.S. Pat. No. 7,145,053 Emenike U.S. Pat. No.6,870,479 Gabriel U.S. Pat. No. 6,603,403 Jeutter U.S. Pat. No.6,774,800 Friedman U.S. Pat. No. 5,903,222 Kawarizadeh U.S. Pat. No.5,469,145 Johnson U.S. Pat. No. 5,264,830 Kline U.S. Pat. No. 7,221,279Nielsen U.S. Pat. No. 8,299,317 Tippey U.S. Pat. No. 9,820,891 Eyall(Light and capacitance) U.S. Pat. No. 9,709,614 Bruwer (Asoteq) U.S.Pat. No. 9,831,864 Thiagarajan (switched cap) U.S. Pat. No. 9,817,537Shakya U.S. Pat. No. 9,811,219 Noto U.S. Pat. No. 7,148,704 Philipp U.S.Pat. No. 6,466,036 Philipp (Atmel) U.S. Pat. No. 4,806,846 Kerber U.S.Pat. No. 2005/0046578A1 Pires U.S. Pat. No. 2007/0024457A1 Long U.S.Pat. No. 2008/0278337A1 Huang U.S. Pat. No. 2009/0124990A1 Feldkamp U.S.Pat. No. 2010/0168694A1 Gakhar U.S. Pat. No. 2015/0080819A1 Charna U.S.Pat. No. 2017/0250661A1 Imaizumi U.S. Pat. No. 2017/0264309A1 Wada U.S.Pat. No. 2017/0308106A1 Ates U.S. Pat. No. 2017/0323134A1 Yeo U.S. Pat.No. 2017/0331366A1 Awad

-   Baby Diaper Wetness Detector and Indicator—A Senior Design Project    from The City College of New York, by Ndaw et al. February 2008-   MTCH112 Dual-Channel Proximity/Touch Controller datasheet by    Microchip Technology Inc., DS41668A-page 28, 2012.

SUMMARY OF THE PRESENT INVENTION

Certain variations of the present invention provide a diaper comprisinga wet diaper monitoring arrangement which is capable of detecting andalerting users when the diaper becomes wet.

Certain variations of the present invention provide a diaper comprisinga first sensor electrode and a second sensor electrode so that when adiaper becomes wet, the capacitance between the first sensor electrodeand the second sensor electrode increases substantially so as totransform the single planar capacitor of the first sensor electrode andthe second sensor electrode into two much larger series connectedcapacitors.

Certain variations of the present invention provide a diaper comprisinga wet diaper monitoring arrangement which utilizes differentalternatives of switch capacitor circuit to detect and determine whetheror not a diaper body has become wet.

In one aspect of the present invention, it provides a diaper,comprising:

a diaper body; and

a wet diaper monitoring arrangement, which comprises:

a disposable pouch detachably attached on a front portion of the diaperbody, the disposable pouch having a receiving cavity; and

a monitoring device, which comprises:

a monitoring casing provided in the receiving cavity at a positionadjacent to an inner surface of the disposable pouch;

a first sensor electrode and a second sensor electrode spacedly providedon an inner surface of and received in the monitoring casing, the firstsensor electrode and the second sensor electrode forming a single planarcapacitor when the diaper body is dry;

a sensing circuitry received in the monitoring casing and electricallyconnected to the first sensor electrode and the second sensor electrode;and

an indicator supported by the monitoring casing and electricallyconnected to the sensor circuitry, wherein when the diaper body becomeswet, a capacitance between the first sensor electrode and the secondsensor electrode increases substantially so as to transform the singleplanar capacitor of the first sensor electrode and the second sensorelectrode into two much larger series connected capacitors, thesubstantial change in the capacitance being arranged to be detected bythe sensing circuitry which drives the indicator to indicate acorresponding wet signal of the diaper.

In another aspect of the present invention, it provides a wet diapermonitoring arrangement for a diaper comprising a diaper body having aninner layer, an outer layer, and an absorbent layer sandwiched betweenthe inner layer and the outer layer, the wet diaper monitoringarrangement comprising:

a disposable pouch configured for affixing on a front portion of thediaper body, the disposable pouch having a receiving cavity; and

a monitoring device, which comprises:

a monitoring casing provided in the receiving cavity at a positionadjacent to an inner surface of the disposable pouch;

a first sensor electrode and a second sensor electrode spacedly providedon an inner surface of and received in the monitoring casing, the firstsensor electrode and the second sensor electrode forming a single planarcapacitor when the diaper body is dry;

a sensing circuitry received in the monitoring casing and electricallyconnected to the first sensor electrode and the second sensor electrode;and

an indicator supported by the monitoring casing and electricallyconnected to the sensor circuitry, wherein when the diaper body becomeswet, the absorbent layer being converted from an insulating layer to aconductive layer so that a capacitance between the first sensorelectrode and the second sensor electrode increases substantially so asto transform the single planar capacitor of the first sensor electrodeand the second sensor electrode into two much larger series connectedcapacitors, the substantial change in the capacitance being arranged tobe detected by the sensing circuitry which drives the indicator toindicate a corresponding wet signal of the diaper.

This summary presented above is provided merely to introduce certainconcepts and not to identify any key or essential features of theclaimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front schematic view of a diaper with an attached wet diapermonitoring arrangement according to a preferred embodiment of thepresent invention.

FIG. 2 is a cross-sectional side view of the diaper with the wet diapermonitoring arrangement according to the preferred embodiment of thepresent invention.

FIG. 3 is a schematic diagram of a monitoring device according to thepreferred embodiment of the present invention, illustrating a PCB andtwo sensor electrodes.

FIG. 4 is a schematic diagram of a wet diaper monitoring deviceaccording to the preferred embodiment of the present invention,illustrating a simplified view of FIG. 2 and two equivalent capacitorsformed by two electrodes when the diaper is wet.

FIG. 5 is a rear view of a disposable pouch according to the preferredembodiment of the present invention.

FIG. 6 is a schematic diagram of a four transistor Switched CapacitorCircuit (SCC) driven by two non-overlapping clocks according to thepreferred embodiment of the present invention.

FIG. 7 is a simplified equivalent circuit of FIG. 6.

FIG. 8 is an alternative SCC circuit diagram according to the preferredembodiment of the present invention.

FIG. 9 is a simplified SCC equivalent circuit of FIG. 8.

FIG. 10 is a timing diagram showing the relationship of the twonon-overlapping clocks for the Switched Capacitor Circuit along with aRESET timing signal according to the preferred embodiment of the presentinvention.

FIG. 11 is a simplified block diagram of the wet diaper monitoringdevice using SCC equivalent circuit according to the preferredembodiment of the present invention.

FIG. 12 is the voltage waveform of the top sensor electrode of FIG. 11.

FIG. 13 is a timing diagram showing the relationship of various signalsand the two non-overlapping clocks.

FIG. 14 is a schematic diagram of a current mirror circuit according tothe preferred embodiment of the present invention.

FIG. 15 is an alternative block diagram of the wet diaper monitoringdevice using SCC equivalent circuit and a current mirror according tothe preferred embodiment of the present invention.

FIG. 16 is the voltage waveform on C int of FIG. 15 according to thepreferred embodiment of the present invention.

FIG. 17 illustrates a software flow chart of the wet diaper monitoringdevice according to the preferred embodiment of the present invention.

FIG. 18 illustrates a first alternative software flow chart of wetdiaper monitoring device according to the preferred embodiment of thepresent invention.

FIG. 19 illustrates a capacitance proximity/touch sensor IC detecting anapproaching finger using a single electrode.

FIG. 20 illustrates a second alternative configuration of the wet diapermonitoring device according to the preferred embodiment of the presentinvention, illustrating that the same capacitance proximity/touch sensorIC is being modified for use as a novel electronic detector to monitor“C sensor” capacitance change by adding an input capacitor to reduce itsanalog input sensitivity.

FIG. 21 illustrates a software flow chart of wet diaper monitoringdevice using a commercially available capacitance proximity/touch sensorIC an electronic detector for this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description of the preferred embodiment is thepreferred mode of carrying out the invention. The description is not tobe taken in any limiting sense. It is presented for the purpose ofillustrating the general principles of the present invention.

Referring to FIGS. 1 to 21 of the drawings, a diaper according apreferred embodiment of the present invention is illustrated. Broadly,the diaper 1 may comprise diaper body 10 and a wet diaper monitoringarrangement 20 provided on the diaper body 10.

The wet diaper monitoring arrangement 20 may comprise a disposable pouch3 and a monitoring device 2. The monitoring device 2 may comprise amonitoring casing 29, a first sensor electrode 7, a second sensorelectrode 8, a sensing circuitry 12, and an indicator 5.

The disposable pouch 3 may be detachably affixed on a front portion 110of the diaper body 10. The disposable pouch 3 may have a receivingcavity 33.

The monitoring casing 29 may be provided in the receiving cavity 33 at aposition adjacent to an inner surface 31 of the disposable pouch 3.

The first sensor electrode 7 and the second sensor electrode 8 may bespacedly provided on an inner surface of and received in the monitoringcasing 29. The first sensor electrode 7 and the second sensor electrode8 may form a single planar capacitor when the diaper body 10 is dry.

The sensing circuitry 12 may be received in the monitoring casing 29 andelectrically connected to the first sensor electrode 7 and the secondsensor electrode 8. The sensing circuitry 12 may be implemented on aPrinted Circuit Board (PCB 13).

The indicator 5 may be supported by the monitoring casing 29 andelectrically connected to the sensor circuitry 12. When the diaper body10 becomes wet, a capacitance between the first sensor electrode 7 andthe second sensor electrode 8 increases substantially so as to transformthe single planar capacitor of the first sensor electrode 7 and thesecond sensor electrode 8 into two much larger series connectedcapacitors, wherein the substantial change in the capacitance may bedetected by the sensing circuitry 12 which drives the indicator 5 toindicate a corresponding wet signal of the diaper of the presentinvention.

In the preferred embodiment of the present invention, FIG. 1 illustratesthe attachment of the wet diaper monitoring arrangement 20 on the diaperbody 10. The first sensor electrode 7 and the second sensor electrode 8may be adapted to detect a soiled condition when urine or other bodyfluid is present in the diaper body 10. The diaper body 10 may beconfigured as having a 3-layer absorbent structure and comprise an innerlayer 9, an absorbent layer 10, and an outer layer 11. The inner layer 9may channel urine or other body fluid away from skin while maintaining adry feeling to the wearer. The absorbent layer 10 may be formed betweenthe inner layer 9 and the outer layer 11 for absorbing urine or the bodyfluid exuded by the wearer. The outer layer 11 may be configured as aprotective layer that keeps urine and body fluid from leaking out. Thediaper body 10 may have a wearing cavity 100 for allowing a wearer towear on, and a plurality of leg openings 101 for allowing the wearer'slegs to pass therethrough. The diaper body 10 may be made of flexibleand soft material for imparting maximal comfort to the wearer.

The disposable pouch 3 of the wet diaper monitoring arrangement 20 maybe made of flexible plastic material and may be shaped and sized forenclosing the monitoring device 2. The disposal pouch 3 may have twoimportant surfaces, an inner surface 31 and an outer surface 32. Theinner surface 31 may be coated with an adhesive layer 6 with a peel-offcover (not shown), while the outer surface 32 may be linked to a flap14. Upon inserting the monitoring device 2 into the pouch 3, the flap 14may be folded over and sealed against the upper edge portion 61 of theadhesive layer 6 forming an enclosed pouch assembly. This enclosed pouchassembly may be affixed to an exterior surface on the front portion 110of the diaper body 10 using the remainder of the adhesive layer 6.

FIG. 5 illustrates the construction details of disposable pouch 3. It isformed by folding a properly shaped and sized piece of plastic sheettogether and then heat sealing the two sides 20, 22 together for forminga pouch structure. Plastic sheet is stretchable and is low cost. Thedisposable pouch 3 may have an opening 23 with a flap 14 and aclosed-end 21. The inner surface 31 may be smaller in area and may behave the adhesive layer 6 coated thereon. The outer surface 32 may beconnected to the flap 14. A perforated line 18 may be incorporated onthe inner surface 31 and the outer surface 32 of the disposable pouch 3.This creates an easy tear-off feature facilitating the retrieval of thewet diaper monitoring device 2 during a diaper change.

During normal use, the monitoring device 2 may be inserted into thedisposable pouch 3 via the opening 23 such that the inner surface of themonitoring casing 29 may be adjacent to the inner surface 31 of thedisposable pouch 3. The flap 14 may then be folded over and sealedagainst the top edge portion 61 of the adhesive layer 6 so as to formthe enclosed pouch assembly. The disposable pouch 3 may be affixed tothe outer surface of the front portion 110 of the diaper body 10 usingthe remainder of adhesive layer 6.

In addition to offering protection against potential urine and fecescontamination, the disposable pouch 3 may be sized so that itsstretchable property may exert a constant compression force onmonitoring device 2 (and the monitoring casing 29) at all time. Thisconstant compression force serves an important function to minimize theformation of any air pocket between disposable pouch 3 and themonitoring casing 29. Since the first sensor electrode 7 and the secondsensor electrode 8 may be mounted in direct contact with the innersurface interior of monitoring casing 29, any air pocket formation couldalter sensor capacitance reading as air has a different dielectricconstant (ϵ=1) than that of the pouch plastic (ϵ approximately equals to2.2). Once an air pocket was inadvertently created, the size of this airpocket may change or move around due to the physical movements of thewearer. The formation or any change in air pocket can create aninaccurate reading on the sensor capacitance value. A constantcompression force may eliminate this possibility.

The disposable pouch 3 may be affixed to an exterior surface on thefront portion 110 of the diaper body 10 using the peel-off adhesivetechnique. The monitoring device 2 may further comprise a pushbutton 4provided on the monitoring casing 29 and electrically connected to thesensing circuitry 12. The indicator 5 may be configured as a LightEmitting Diode (LED) and may provide a visual operating status of themonitoring device 2. For example, a slow blinking green color generatedby the LED may indicate that monitoring device 2 is operating normallyand the diaper body 10 is dry. A fast blinking red color generated bythe LED may indicate that the diaper body 10 is wet and needs to bechanged. Furthermore, an alternating red and green blinking generated bythe LED may indicate that the battery level is low and the battery needsto be replaced.

The pushbutton 4 may be configured as a momentary switch forinitializing a new monitoring process after completing a diaper change.Upon activation, software program (described below) of the monitoringdevice 2 may perform four consecutive capacitance sensor readings andsaves the average of these four readings as the digital baselinereference value. All future sensor readings will be compared againstthis reference value. The mechanism of these calculation will bedescribed in more details below.

Referring to FIG. 2 of the drawings, it illustrates that the monitoringdevice 2 may be enclosed within the disposable pouch 3 and then sealedby using the flap 14. This forms an enclosed pouch assembly. Themonitoring casing 29 may have a first casing surface 291 and a secondcasing surface 292. The first casing surface 291 may be defined as theinner surface that is placed closest to the diaper body 10 while thesecond casing surface 292 may be defined as the outer surface which isopposite to the first casing surface 291.

The first sensor electrode 7 and the second sensor electrode 8 may beetched on one side of the PCB 13 and are placed in direct contactagainst the first casing surface 291 of the monitoring casing 29. Thesensing circuitry 12 may comprise a plurality of electronic componentswhich will be described below. The electronic components may be mountedon the PCB 13 and may be oriented away from the first sensor electrode 7and the second sensor electrode 8. FIG. 3 illustrates a front view ofthe first sensor electrode 7 and the second sensor electrode 8, eachmeasuring approximately 10 mm by 25 mm in surface area and spaced 5 mmfrom each other.

There are different methods to evaluate a new sensor reading by thesoftware program. A simple method is to compare the new reading againstthe digital baseline reference value to determine wetness level. Forexample, the diaper body 10 is deemed to be soiled if a new readingexceeds the digital baseline reference value by 50% (or other percentagevalue as appropriate). The software flow chart of this method may beillustrated in FIG. 17. An alternate software flow chart may beillustrated in FIG. 18, where the average of the four latest sensorreadings is calculated and saved as the new base-reference value. Thisapproach can compensate for slow change due to temperature effect. Sincea soiled diaper is likely to stay wet for a while, note that bothsoftware flow charts require the soiled condition to last at least3-seconds or longer before activating alerting outputs.

Instead of comparing against a calculated digital baseline reference, aneven simpler method is for each new reading to be compared against afixed digital number imbedded in the software program. If a new readingexceeds this fixed digital number by a fixed value or more, then thediaper is soiled. When a soiled condition is detected, software programmay activate the indicator 5 to show red color while simultaneously sendout a wireless signal via a built-in wireless RF transmitter 25.Additional audio alerting device such as a speaker can also be activatedfor local alerting. Thus, the monitoring device 2 may further comprise awireless Radio Frequency (RF) transmitter 25 electrically connected tothe sensing circuitry 12 for transmitting RF signal.

Software program may determine how frequent a new reading is to betaken. To minimize battery drain, the software program can vary theperiod between readings according to a simple variable time format. Forexample, the software program may initiate a new reading every 10minutes during the first 30 minutes after a diaper change, then changeto performing a new reading every five (5) minutes during the next 30minutes, and finally change to performing a new reading every minuteuntil a soiled diaper condition is detected. The software program isflexible enough so the parent or a caretaker can override this variabletime reading format to a constant one (1) minute reading format. A userof the present invention may accomplish this by pressing and holding thepushbutton 4 for a predetermined period of time (such as 10 seconds)until the software program acknowledges this change by providing atemporarily blinking green color through the indicator 5. Moreover,pressing and holding the pushbutton 4 for another predetermined periodof time may toggle the setting back to the variable time reading formatagain. Thus, the user of the present invention may be set to be in fullcontrol of selecting the most effective reading interval for eachindividual circumstance.

As an exemplary embodiment, when the diaper is dry, the planarcapacitance between the two sensor electrodes may be estimated using thefollowing formula:

C=ϵoϵr(t*l)/d, where

ϵo=permittivity in vacuum=8.85 pf/m

ϵr=relativity permittivity (dielectric constant)=4.4 (for FR4 PCB)

t=the thickness of the electrode=0.035 mm (base on a 1 oz copper PCB)

l=the length of the electrode=25 mm

d=the separation distance between the electrodes=5 mm

C=0.0068 pf, in which this is an extremely small value and circuitparasitic capacitance will dominate. Parasitic in the range of up to 2pf is expected in real circuit operation.

Dry diaper sensor capacitance=C dry=parasitic capacitance=2 pf

Urine is a good conductor. When the diaper body 10 becomes wet, theabsorbent layer 10 may change from an insulator layer to a conductivelayer. This effectively changes a single planar capacitor into two largeseries connected capacitors as shown in FIG. 4. A new capacitor isformed between each electrode and the wet absorbent layer 10, separatedby insulator layer 11. The surface area of each of the two newcapacitors is 250 sq. mm which is 285 times larger than that of theoriginal planar capacitor. Therefore, a wet diaper transforms the firstsensor electrode 7 and the second sensor electrode 8 from a singleplanar capacitor into two much larger series connected capacitors.

FIG. 4 illustrates a simplified view of FIG. 2 when the diaper body 10is wet. As shown in FIG. 4 of the drawings, K represents the totalthickness of the disposable pouch 3 and the monitoring casing 29, theadhesive layer 6, and the outer layer 11 of the diaper body 10. Thefirst sensor electrode 7 and the second sensor electrode 8 may bearranged to make direct contact against the monitoring casing 29 so thatthere is no air gap between the first and the second sensor electrode 7,8 and the monitoring casing 29. This arrangement may minimize k andmaximize ϵr on the capacitance formula below, and may produce a largersensor capacitance change when the diaper body 10 changes from dry towet. The first sensor electrode 7 and the second sensor electrode 8 andthe inner layer 10 of the diaper body 10 may form two equivalentcapacitors, C-eq1 and C-eq2 as shown below.

The capacitance, C, of the two electrodes shown in FIG. 4 can beestimated using the following formula:

C=C-eq1=C-eq2=ϵoϵr(x*l)/d

Where,

ϵo=permittivity in vacuum=8.85 pf/m

ϵr=relativity permittivity (dielectric constant) of layer k˜=2.2 (forplastic)

x=the width of the electrode=10 mm

l=the length of the electrode=25 mm

d=K=the distance between each electrode to the wetted diaper layer˜=0.75 mm

C=6.5 pf for each electrode; or C wet=3.25 pf total since they are inseries.

Wet diaper sensor capacitance=C wet+C dry=3.25 pf+2 pf=5.25 pf

In this preferred embodiment, the present invention utilizes a SwitchCapacitor Circuit (SCC) that consists of a single capacitor, twotransistors, and two non-overlapping clock signals for converting asensor capacitance into a digital equivalent value suitable for digitalsignal processing. A switched capacitor circuit (SCC) is an electroniccircuit technique used for discrete-time signal processing. SCC works bymoving charges of an electrical-signal into and out of capacitors whentransistor switches are opened and closed by clock signals. Usually,non-overlapping clock signals are used to control the transistorswitches, so that not all switches are closed simultaneously.

FIG. 6 of the drawings illustrates a Switched Capacitor Circuit (SCC) 14using four transistor switches M1, M2, M3, M4 (first through fourthtransistor switch), one capacitor C1 and two non-overlapping clock CLK1,CLK2 (first non-overlapping clock and second non-overlapping clock).Each of the four transistors M1, M2, M3, M4 may have a Drain terminal, aGate terminal, and a Source terminal. Its equivalent circuit 15 is shownin FIG. 7 of the drawings where four mechanical switches are used torepresent the four transistors M1, M2, M3, M4. The timing relationshipof the two non-overlapping clocking signals (CLK 1 and CLK 2) are shownin FIG. 10 of the drawings. CLK 1 and CLK 2 may control the Gateterminal of each transistor switch M1, M2, M3, M4. Note that when CLK 1is high, CLK 2 is always low and vice versa. Both clock signals from CLK1 and CLK 2 cannot be high at the same time, but both can be low at thesame time. This non-overlapping clock relationship ensures that the SCCwill have no signal leakage between its input terminal to its outputterminal. When the clock signal is high, the connected transistors M1,M2, M3, M4 will be on or become conductive between the correspondingDrain and Source terminals. When the clock signal is low, the connectedtransistors M1, M2, M3, M4 will be off or non-conductive between thecorresponding Drain and Source terminals. SCC 14 has two input terminals141, 142 and two output terminals 143, 144, so it can process bothdifferential and single-ended input/output signals. The clocking actionof the SCC causes capacitor C1 to transfer charge from one circuit node(input) to a different circuit node (output).

In FIG. 8, SCC 16 represents an alternative circuit where the bottomplate of capacitor C1 is either connected to circuit ground or to areference voltage. Its equivalent circuit 17 is shown in FIG. 9 of thedrawings and it can only process a single-ended input and outputsignals. Thus, SCC 16 may have one input terminal 161 and one outputterminal 162. The input terminals and the output terminals of both SCC14 and the alternative SCC 16 are symmetrical. Therefore, the input andthe output terminals of each SCC 14, 16 may be interchangeable. That is,each of the input terminals may be used as an output terminal andvice-versa, depending on layout convenience.

Circuit operation of SCC 14 of FIG. 6 will be described in detail nowwith the help of the equivalent circuit 15 as shown in FIG. 7 inconjunction with CLK 1 and CLK 2 of FIG. 10. When CLK 1 goes high whileCLK 2 is at low, switches M1 and M3 are closed, while switches M2 and M4are open, so the difference between the input voltage of the inputterminal 141 (Vin-In 1) and the input voltage of another input terminal142 (Vin-In 2) is being sampled by C1. When CLK 1 goes low and CLK 2stays low, all switches (M1, M2, M3, M4) are open so C1 stores a chargecorresponds to the sampled value difference between (Vin-In 1) and(Vin-In 2). The charge stored in C1 is:

Q=C×V=(C1)*((Vin-In1)−(Vin-In2)).

On the other hand, when CLK 2 goes high and CLK 1 stays low, theswitches M2 and M4 are closed while M1 and M3 remain open, therefore, C1is connected to its output nodes (the two output terminals 143, 144) andthe stored charge on C1 is being made available for processing byanother circuit connecting to the output terminals 143, 144 (Out 1 andOut 2). Circuit operation repeats during the next CLK 1 and CLK 2 clockinterval and so on. The foregoing discussion of equivalent circuit 15 ofFIG. 5 can be summarized in Table 1 below:

TABLE 1 Step Clock states Switch States Circuit Action Note 1 CLK 1 =Hi, M1, M3 = close, C1 samples ((Vin-In 1)- CLK 2 = Lo M2, M4 = open(Vin-In 2) 2 CLK 1 = Lo, M1, M2, M3, C1 stores Q = (C1) * CLK 2 = Lo M4= open ((Vin-In 1)-(Vin-In2)) 3 CLK 1 = Lo, M1, 3 = open, C1 connects toOut 1 & CLK 2 = Hi M2, 4 = close Out 2; outputs Q 4 CLK 1 = Hi, M1, 3 =close, C1 samples ((Vin-In 1)- Repeat of CLK 2 = Lo M2, 4 = open (Vin-In2) Step 1 6 CLK 1 = Lo, M1, 2, 3, 4 = open C1 stores Q = (C1) * Repeatof CLK 2 = Lo ((Vin-In 1)-(Vin-In2)) Step 2 7 CLK 1 = Lo, M1, 3 = open,C1 connects to Out 1 & Repeat of CLK 2 = Hi M2, 4 = close Out 2; outputsQ Step 3

SCC 16 of FIG. 8 will be described in detail now using the equivalentSCC circuit 17 as shown in FIG. 9 in conjunction with CLK 1 and CLK 2 ofFIG. 10. When CLK 1 goes high while CLK 2 is at low, switch M5 closes,while switch M6 stays open, so the input voltage of the input terminal161 (Vin-In 1) is being sampled by C1. When CLK 1 goes low and CLK 2stays low, both switches M5 and M6 are open so C1 stores a chargecorresponds to the sampled value of Vin-In 1. The charge stored in C1is:

Q=C×V=(C1)*(Vin-In11).

When CLK 2 goes high while CLK 1 stays low, Switch M6 closes while M5remains open, C1 is connected to its output node (Out 1) and the storedcharge is being made available for processing by another circuitconnecting to the output terminal 162. Circuit operation repeats duringthe next CLK 1 and CLK 2 clock intervals and so on. The foregoingdiscussion of the equivalent SCC circuit 17 in FIG. 9 can be summarizedin Table 2 below:

TABLE 2 Step Clock states Switch States Circuit Action Note 1 CLK 1 =Hi, M5 = close, C1 samples ((Vin-In 1)- CLK 2 = Lo M6 = open 2 CLK 1 =Lo, M5 = open, C1 stores Q = (C1) * CLK 2 = Lo M6 = open ((Vin-In 1) 3CLK 1 = Lo, M5 = open, C1 connects to Out 1 CLK 2 = Hi M6 = close andoutputs Q 4 CLK 1 = Hi, M5 = close, C1 samples ((Vin-In 1) Repeat of CLK2 = Lo M6 = open Step 1 6 CLK 1 = Lo, M5 = open C1 stores Q = (C1) *Repeat of CLK 2 = Lo M6 = open (Vin-In 1) Step 2 7 CLK 1 = Lo, M1, 3 =open, C1 connects to Out 1 Repeat of CLK 2 = Hi M6 = close and outputs QStep 3

The block diagram of the preferred embodiment of the monitoring device 2may be illustrated in FIG. 11 of the drawings. The block diagram maycomprise a capacitance sensor (C sensor 22), a SCC equivalent circuit17, a comparator 27, a Counter/Register and Control Logic (CRCL 28), atransistor reset switch (M7), a battery supply 23, the Reset/Testpushbutton 4, the LED Indicator 5, a speaker 24, and a RF Transmitter25.

Note that the capacitor, the transistors, the digital clock circuit, thedigital registers/counters, and the comparator are standard buildingblocks available in any MOS technology and process. The use of thesestandard MOS building blocks means the complete block diagram of FIG. 9,except for C sensor 22, can be integrated onto a single silicon dieusing standard MOS manufacturing process. Integrating a complete systemor block diagram onto a single silicon die may save production costwhile ensuring a more consistent product performance.

The following discussion covers in detail how a sensor capacitance (ananalog value) is converted into a digital equivalent value using thearrangement shown in FIG. 11 of the drawings.

A conversion cycle to transform the sensor capacitance into a digitalequivalent value requires many clock operations. A clock operation maybe referred to all circuit functions or operations performed during theperiod consisting of a CLK 1 pulse and a CLK 2 pulse. A typicalconversion may require anywhere from 50 to 500 clock operations. Bydesign, the number of clock operations required is proportional to thecapacitance ratio between C sensor 22 to C1 of the SCC 17. Circuitoperation of the embodiment in FIG. 11 may be described by using thetiming signals of FIG. 13 of the drawings. “Reset” signal is a periodicpulse generated by CRCL 28 to initiate conversion cycle. Its frequencyis controlled by the software program. For example, the software programmay initiate a new conversion every 60 seconds. This “Reset” signalindicates the beginning of a conversion cycle by initializing allinternal registers and counters while charging C sensor 22 to Vcc viaSwitch M7. Therefore, the charge stored across C Sensor 22 at thebeginning of a conversion cycle is:

Q0=C Sensor*Vcc.

CRCL 28 also brings “Enable” to high, at the beginning of “Reset”signal, so Comparator 27 is enabled for voltage comparation during aconversion cycle. The timing relationship between “Reset” signal,“Enable” signal and Comparator 27 output is illustrated in FIG. 13.After “Reset” signal goes high, “CLK 2” stays high to discharge C1 toground via Switch M6 of SCC 17. The voltage input at the “−” terminal ofComparator 27 is higher than the voltage at its “+” terminal soComparator 27 output is low. After “CLK 2” goes low and then “CLK 1”goes high, C 1 is paralleled across C Sensor 22 by Switch M5. A smallportion of the charge stored on C Sensor 22 will be redistributed to C1,so Q0=(C Sensor×Vcc)=(C Sensor+C 1)×V C sensor, where “V C sensor” isthe new voltage reading on C sensor 22 after charge redistribution withC1. Note that, by design, C1 will be hundreds of times smaller than thecapacitance value of C Sensor 22. So, V C sensor is only slightly lessthan its previous reading but is still substantially higher than ⅓ Vcc.Therefore, Comparator 27 output is low while “Enable” is high. Duringthis unique logic state, each positive transition of “CLK1” incrementsthe content of a special digital counter in CRCL 28 by one-count. Thisspecial counter keeps track of the total number of “CLK 1” pulsesoccurred in a conversion cycle.

When “CLK 1” goes low and the next “CLK 2” goes high, C1 is dischargedto ground again by switch M6 while the voltage on C Sensor 22 sees nochange. When “CLK 2” goes low and then “CLK 1” goes high again, C1 isparalleled across C Sensor 22 again to redistribute the remainingcharge. This forces the V C sensor to go slightly lower again. Theforegoing discharging and then charge redistribution process continuesuntil V C sensor finally falls below ⅓ Vcc so the output of Comparator27 switches from low to high. The voltage waveform across C Sensor 22follows its classical exponential decay pattern and reaches below ⅓ Vccat t1 as shown in FIG. 12 of the drawings. This decay time isproportional to the capacitance value of C sensor 22. The Comparator 27output transition is captured by the logic circuit of CRCL indicatingend-of-conversion. In turn, CRCL 28 would disable Comparator 27 fromfurther operation by bringing “Enable” low. CRCL 28 also saves thecontent of the special digital counter that keeps track of the totalnumber of “CLK 1” pulses. The content of this special digital counter atthe end-of-conversion represents the digital equivalent value of thecapacitance value of C Sensor 22.

After a diaper change and pressing of the “Reset/Test” pushbutton 4, thesoftware program may initiate four consecutive conversion cycles to comeup with four digital equivalent values, so an average digital value maybe calculated. This averaged digital value is saved as a baselinereference value for comparison against new conversion results. At theend of each new conversion, the new digital equivalent value will becompared against the baseline reference value. If the new digitalequivalent value exceeds the baseline reference value by apre-determined percentage, CRCL 28 sets an internal flag signaling asoiled diaper condition is detected. Under software control, CRCL 28 cansignal a LED indicator 5 and a speaker 24 for local alerting for apredetermined period or until the Reset/Test pushbutton 4 is pressed.Simultaneously, CRCL 28 may also activates RF Transmitter 25 to send outa wireless signal to notify any wireless receiver (not shown). CRCL 28also keeps track of the elapse time when the soiled condition was firstdetected. If the soiled diaper is not changed within 5 minutes, CRCL 28would send out a more urgent reminder wireless signal to alert thewireless receiver.

Software program can be implemented such that a new baseline referencevalue is established by calculating the running average of the latestfour conversion results or readings. A new running baseline referencevalue obtained in this fashion can offset any slow sensor capacitancechanges due to temperature effect.

As shown in FIG. 15 of the drawings, an alternative circuit diagram ofthe monitoring device 2 is illustrated. As shown in FIG. 15, the SCCequivalent circuit 15 may comprise a C sensor 22 as the switchedcapacitor, a current mirror 26, an internal capacitor C int 180, acomparator 27, a Counter/Register and Control Logic (CRCL) 28, atransistor reset switch (M10), a battery supply 23, a Reset/TestPushbutton 4, a LED Indicator 5, a speaker 24, and a RF Transmitter 25.

Switching C sensor 22 at a fixed clock rate produces an equivalentresistor according to the relationship:

R equivalent=1/(C sensor*F clk)

Since C sensor 22 is typically many times larger than any capacitorfabricated on a silicon chip, switching C sensor 22 at the same clockrate would produces a lower impedance across C sensor 22 than otherwise.The advantage of lower impedance means it would be less sensitive to anyexternal noise effect or electrical interference.

Note that the internal capacitor, the transistors, the digital clockcircuit, the digital registers/counters, and the comparator mentionedabove may be standard MOS building blocks which may be integrated onto asingle silicon die using standard MOS manufacturing process. Integratinga complete system or block diagram onto a single silicon die savesproduction cost while ensuring a more consistent product performance.

The following discussion covers in detail how a sensor capacitance (ananalog value) is converted into a digital equivalent value using theblock diagram embodiment of FIG. 15.

A conversion cycle to transform the sensor capacitance into a digitalequivalent value requires many clock operations. A clock operation meansall circuit functions or operations performed during the periodconsisting of a CLK 1 pulse and a CLK 2 pulse. A typical conversion mayrequire tens to hundreds of clock operations. For this alternativecircuit diagram of FIG. 15, C sensor 22 is part of SCC 15 and is beingswitched by switches M1, M2, M3, and M4 under the control of CLK 1 andCLK 2. Its output is connected to the input terminal of a current mirror26. A current mirror 26 is needed to reduce this large input currentinto a much smaller current, so a small internal capacitor, C int 180,can be charged or discharged in a reasonable time. The current mirror 26may comprise two MOS transistors connected as shown in FIG. 14 where thetwo gates are tied to the same bias voltage. Under this condition, theirdrain current ratio is proportional to their respective “gate width” to“gate length” ratio or W/L ratio. By controlling this W/L ratio and bysetting the input current, a controlled output current can be derivedaccording to the following input-output relationship:

N=I out/I in =W/L output:W/L input, where Nis set to 0.01 in thispreferred embodiment.

The circuit operation of this second embodiment, FIG. 15, can best bedescribed using the timing signals of FIG. 13. “Reset” signal is aperiodic pulse generated by CRCL 28 and its frequency is controlled bythe software program. This “Reset” signal indicates the beginning of aconversion cycle by initializing all internal registers and counters.CRCL 28 also brings “Enable” to high, so the comparator 27 may beenabled for voltage comparation. The timing relationship between the“Reset” signal, the “Enable” signal and the comparator 27 output isillustrated in FIG. 13 of the drawings. C int 180 is initially shortedto Vcc by switch M10.

Switching a capacitor, C sensor 22, at a fixed clock rate produces anequivalent resistor. Therefore, SCC 15 behaves as a resistor accordingto the following relationship:

R equivalence=1/(f*C sensor), where f=CLK 1 frequency=CLK 2 frequency

Thus, SCC 15 may set a constant input current to current mirror 26. Theoutput of current mirror 26 is also constant but at 100 times smaller bydesign. This constant output current discharges the voltage on C int 180according to the following relationship:

Δ Voltage=(1/C int)*I out*Δt)

Therefore, the voltage across C int 180 drops linearly from Vcc towardground as shown in FIG. 16. The comparator 27 output stays low until thevoltage on C int 180 drops just below ⅓ Vcc at t1. At that point, itsoutput switches from low to high. This output transition informs CRCL 28that conversion is complete. CRCL 28 immediately brings “Enable” signallow to disable Comparator 27 until the beginning of the next conversioncycle. A special digital counter inside CRCL 28 keeps track of the totalnumber of “CLK 1” pulses occurred during a conversion while “Enable”signal is high. The content of this special digital counter at theend-of-conversion represents the digital equivalent value of thecapacitance value of C Sensor 22.

Base on the nominal design value of a 5.25 pf sensor capacitance (whendiaper is wet) and a clock rate of 100 Khz, a 1 pf value is needed for Cint 180. It would take about 200 μsec (or 20 clock cycles) for thevoltage on C int 180 to drop from 3 volt to 1 volt in FIG. 16, assumeVcc=3 volt. The calculations to derive 200 μsec are shown below:

Current mirror input current=I in =(Vcc−V threshold)/R1=(Vcc−1 v)/Requivalence, where V threshold is the current mirror input thresholdvoltage ˜1 volt for a MOS transistor, and R equivalence=1/(100 Khz*5.25pf)˜2 Meg.

Therefore, Current mirror input current=I in =(3 v−1 v)/2 Meg=1 μA andCurrent mirror output current=I out=0.01*I in =0.01 μA.

Δ Voltage at C int 180=(1/C int)*I out*Δt

Δ Voltage at C int 180=(Vcc−⅓Vcc)=(I out*Δt)/C int 180

⅔Vcc=(0.01ua*Δt)/1 pf

Δt=(⅔*3.0 v*1 pf)/0.01 μA

Δt=2*1 pf/0.01 μA

Δt=200 μsec

Number of clock cycle=Digital equivalent value=Δt/Clock period

Digital equivalent value=200 μsec/( 1/100Khz)=20 (for a wet diaper)

Similar calculations carrying out to determine the digital equivalentvalue for a dry diaper with a 2 pf parasitic capacitance is 52. Thus,there is a greater than 60% decrease in digital equivalent value whenthe diaper changes from a dry condition to a wet condition.

After a diaper change and at the press of “Reset/Test” pushbutton 4, thesoftware program would initiate four consecutive conversion cycles tocome up with four digital equivalent values, so an average digital valuecan be calculated. This averaged digital value is saved as a baselinereference value for comparison against new conversion results orreadings.

A wetted diaper causes C sensor 22 capacitance to increase. This wouldcause R equivalence to decrease. This increases the input current to thecurrent mirror 26 and would speed up the discharging of C int 180. Thisshortens t1 in FIG. 16 and results in a smaller digital equivalent valueaccumulated in the special digital counter. A comparison of this newvalue against a baseline reference value is performed. If the differenceexceeds a pre-determined percentage (>=30%), CRCL 28 sets an internalflag signaling a soiled diaper condition is detected. Under softwarecontrol, CRCL 28 can signal the LED indicator 5 and the speaker 24 forlocal alerting for a predetermined period or until the Reset/Testpushbutton 4 is pressed. Simultaneously, the CRCL 28 may also activatethe RF Transmitter 25 sending out a wireless signal to notify anywireless receiver (not shown). The software flow chart in FIG. 17illustrates the approach.

As an additional feature, the CRCL 28 may also keep track of the elapsetime when the soiled condition was first detected. If the soiled diaperis not changed within 5 minutes, CRCL 28 would send out a more urgentreminder wireless signal to alert the wireless receiver.

Software program can also be implemented such that a running newbaseline reference value can be established by calculating the averageof the latest four conversion results or readings. A new runningbaseline reference value obtained in this fashion can offset slow sensorcapacitance changes due to temperature effect. The software flow chartof FIG. 18 illustrates this running baseline reference value methodwhere the average of the four latest sensor readings is calculated andset as the new baseline reference value.

As a second alternative mode of the present invention as shown in FIG.20 of the drawings, the wet diaper monitoring device 2 may use anabundantly available low-cost capacitance proximity/touch sensorintegrated circuit (IC) chip 36 as the electronic detector for thedetection of the wet diaper sensor capacitance change. This represents anovel application of a capacitance proximity/touch sensor IC which istypically used for human-machine touching interface. This approach usesan off-the-shelf electronic component, which may offer significant costadvantage since no custom chip is needed. FIG. 19 shows the applicationof a commercially available capacitance proximity/touch sensor IC indetecting a finger touch for human-machine interface using a singlesensor electrode 35. When capacitance proximity/touch sensor IC 36detects a sudden increase in capacitance change, it momentarilyactivates LED 37 as a positive response indication. With the popularityof smart phone, tablet computer, ATM, and vending machine sky rocketing,many capacitance proximity/touch sensor ICs are now available for touchsensing applications. These ICs, such as a Microchip's MTCH 112, TI'sFDC 1004, Standard Microsystems' STM8T141, Rohm's BU21077MUV, Azoteq IQS118, Semtech's SX9500, Silicon Labs' CPT007B are designed to detect avery small increase in capacitance. For example, MTCH112 datasheetindicates it can detect a finger approaching from few inches away.Datasheet indicates that capacitance change less than a fraction of apico-farad is detectable by such devices. However, if a capacitanceproximity/touch sensor IC 36 is connected directly to a wet diapermonitoring device capacitance sensor, capacitance proximity/touch sensorIC 36 can be easily false triggered by the normal body movements of thediaper wearer. Therefore, its sensitivity and response time must becontrolled so it is not sensitive to body movement but sensitive to awet diaper condition. Experiment has shown that adding capacitor 39 tothe input pin of capacitance proximity/touch sensor IC 36 can swamp outany stray capacitance variations caused by normal body movements of awearer. This effectively reduces analog input sensitivity.

The response time, digital sensitivity and digital threshold of mostcommercially available capacitance proximity/touch sensor IC areadjustable. Experiment has shown that the combination of a slowerresponse time, a lower digital sensitivity, and a higher digitalthreshold setting is essential to configuring the IC as an electronicdetector of wet diaper detection.

A standard micro-controller 38 is used to interfacing with capacitanceproximity/touch sensor IC 36 and other input-output controls (4, 5, 24,and 25). Micro-controller 38 interfaces with capacitance proximity/touchsensor IC 36 using standard serial bus interface. The firmware of themicro-controller programs the digital sensitivity, digital threshold andresponse time of capacitance proximity/touch sensor IC 36 to theirproper level so any C sensor 22 capacitance change due to the physicalmovement of a wearer cannot cause false triggering while still sensitivein detecting a wet diaper situation. It is also possible that thecommercial available capacitance proximity/touch sensor IC can befactory preprogrammed with the desired digital settings so that themicro-controller is only required to monitor its output. The combinationof analog sensitivity reduction, slower response time, and lower digitalsensitivity/higher digital threshold setting ensures a valid outputsignal only when C sensor 22 encounters a wet diaper condition. Undersoftware control, micro-controller 38 can signal a LED indicator 5 and aspeaker 24 for local alerting for a predetermined period or until theReset/Test pushbutton 4 is pressed. Simultaneously, micro-controller 38also activates RF Transmitter 25 sending out a wireless signal to notifyany wireless receiver (not shown). The software flow chart of this thirdembodiment is illustrated in FIG. 21 where the digital gain and digitalthreshold of capacitance proximity/touch sensor IC 39 is updated whenpushbutton 4 is activated after a diaper change.

As an additional feature, the micro-controller 38 also keeps track ofthe elapse time when the soiled condition was first detected. If thesoiled diaper is not changed within 5 minutes or other preset time,micro-controller 38 would send out a more urgent reminder wirelesssignal for alerting.

This invention has been disclosed and described herein in terms ofpreferred configurations and methods. However, it will be obvious tothose of skill in the art that numerous variations of the illustratedembodiments could be implemented within the scope of this invention. Forexample, a four-phase non-overlapping clocks may be used for SCCclocking instead of a two-phase clock, or a capacitor array may be usedinstead of a single capacitor SCC. Or a modified capacitanceproximity/touch sensor IC with periodic calibration feature could beimplemented within the scope of this invention. These and othermodifications might well be made to the exemplary embodimentsillustrated herein without departing from the spirit and scope of theinvention.

The present invention, while illustrated and described in terms of apreferred embodiment and several alternatives, is not limited to theparticular description contained in this specification. Additionalalternative or equivalent components could also be used to practice thepresent invention.

What is claimed is:
 1. A wet diaper monitoring arrangement for a diapercomprising a diaper body having an inner layer, an outer layer, and anabsorbent layer sandwiched between said inner layer and said outerlayer, said wet diaper monitoring arrangement comprising: a disposablepouch affixed on a front portion of said diaper body, said disposablepouch having a receiving cavity; and a monitoring device, whichcomprises: a monitoring casing provided in said receiving cavity at aposition adjacent to an inner surface of said disposable pouch; a firstsensor electrode and a second sensor electrode spacedly provided on aninner surface of and received in said monitoring casing, said firstsensor electrode and said second sensor electrode forming a singleplanar capacitor when said diaper body is dry; a sensing circuitryreceived in said monitoring casing and electrically connected to saidfirst sensor electrode and said second sensor electrode, said sensingcircuitry comprising: a touch sensor IC electrically connected to saidfirst sensor electrode and said second sensor electrode, said touchsensor IC being configured as an electronic detector to determine if thecapacitance between said first sensor electrode and said sensorelectrode is greater than a predetermined threshold value, said touchsensor IC comprising: an analog input terminal for connection to saidfirst sensor electrode; a reference terminal for connection to saidsecond sensor electrode; a capacitor connected between said analog inputterminal and said reference terminal to reduce an input sensitivity sothat said sensor IC is insensitive to insignificant capacitance change,but responsive to substantial capacitance change caused by a wet diapersituation; a plurality of digital input terminals for accepting digitalcommands from an external controller, said digital commands alteringsaid digital sensitivity, digital threshold, and response time so as tocause said sensor IC to become insensitive to insignificant capacitancechange but responsive to substantially capacitance change caused by saidwet diaper situation; at least one digital output terminal to indicatewhether or not if a capacitance between said first sensor electrode andsaid second sensor electrode exceeds said predetermined capacitancelevel, wherein when said capacitance exceeds said predeterminedcapacitance level, said digital output terminal is arranged to changelogic state to alert said wet situation of said diaper.
 2. The wetdiaper monitoring arrangement, as recited in claim 1, wherein saiddisposable pouch has an inner surface, an outer surface and a flap, saidinner surface being coated with an adhesive layer, while said outersurface being linked to said flap in such a manner that when saidmonitoring device is inserted into said pouch, said flap is folded tocover and seal said receiving cavity of said disposable pouch.
 3. Thewet diaper monitoring arrangement, as recited in claim 2, wherein saiddisposable pouch is configured to be flexible and stretchable so as tonormally exert a constant compression force against said monitoringdevice for preventing formation of air pocket between said disposablepouch and said monitoring casing.
 4. The wet diaper monitoringarrangement, as recited in claim 3, wherein said monitoring devicefurther comprises a pushbutton provided on said monitoring casing andelectrically connected to said sensing circuitry, said pushbutton beingconfigured as a momentary switch for initializing a new monitoringprocess after completing a diaper change.
 5. The wet diaper monitoringarrangement, as recited in claim 4, wherein said monitoring casing has afirst casing surface and a second casing surface, said first casingsurface being defined as a surface that is formed closest to said diaperbody, said second casing surface being defined as a surface which isopposite to said first casing surface, said first sensor electrode andsaid second sensor electrode being electrically connected to saidsensing circuitry and positioned to be in direct contact with said firstcasing surface of said monitoring casing.
 6. The wet diaper monitoringarrangement, as recited in claim 5, wherein said monitoring devicefurther comprises a wireless Radio Frequency transmitter electricallyconnected to said sensing circuitry for wirelessly transmitting radiofrequency signal when said sensing circuitry detects that said diaperbody is wet.
 7. The wet diaper monitoring arrangement, as recited inclaim 6, wherein said disposable pouch is fabricated using by the samematerial as said outer layer of said diaper body.
 8. The wet diapermonitoring arrangement, as recited in claim 7, wherein said disposablepouch is pre-fabricated on said outer layer of said diaper body.